A method of forming a reticulated hook element is disclosed in U.S. Pat. No. 4,001,366 which describes forming hooks by known methods, similar to that disclosed in U.S. Pat. Nos. 4,894,060 and 4,056,593, discussed below. A reticulated web or mesh structure is formed by intermittently slitting (skip slit) extruded ribs and bases and then pulling to expand the skip slit structure into a mesh.
U.S. Pat. No. 5,891,549 describes a method for forming a net sheet having surface protrusions thereon. The net is used primarily as spacer elements for drainage and like applications. The net has parallel elements that extend at right angles to each other and it would appear to be formed by a direct molding process involving directly extruding the net-like structure onto a negative mold of the netting.
A film extrusion process for forming hooks is proposed, for example, in U.S. Pat. Nos. 4,894,060 and 4,056,593, which permits the formation of hook elements by forming rails on a film backing. Instead of the hook elements being formed as a negative of a cavity on a molding surface, as is the more traditional method, the basic hook cross-section is formed by a profiled film extrusion die. The die simultaneously extrudes the film backing and rib structures. The individual hook elements are then preferably formed from the ribs by cutting the ribs transversely, followed by stretching the extruded strip in the direction of the ribs. The backing elongates but the cut rib sections remain substantially unchanged. This causes the individual cut sections of the ribs to separate each from the other in the direction of elongation forming discrete hook elements. Alternatively, using this same type extrusion process, sections of the rib structures can be milled out to form discrete hook elements. With this profile extrusion, the basic hook cross section or profile is only limited by the die shape and hooks can be formed that extend in two directions and have hook head portions that need not taper to allow extraction from a molding surface.